Natural Hazards

, Volume 63, Issue 1, pp 101–117 | Cite as

Probable tsunami origin for a Shell and Sand Sheet from marine ponds on Anegada, British Virgin Islands

  • Eduard G. Reinhardt
  • Jessica Pilarczyk
  • Alyson Brown
Original Paper


A distinctive Shell and Sand Sheet found beneath the marine ponds of Anegada, British Virgin Islands, was formed by a post-1650 AD overwash event, but its origin (tsunami or hurricane) was unclear. This study assesses the taphonomic characters of the shell and large clast material (>2 mm) to determine its provenance and origin. Pond-wide stratigraphic units (Shelly Mud, Shell and Sand Sheet, Mud Cap) were analyzed (12 samples) at four sites in Bumber Well and Red Pond along with eight samples from the Shell and Sand Sheet in a 2-km transect of Bumber Well. Mollusks in the pond muds include Anomalocardia spp. and cerithids with no allochthonous shells from the offshore reef-flat. Results show that the shells and clasts (>2 mm) are derived from the erosion and winnowing of the underlying Shelly Mud of the former marine pond, forming a distinctive sheet-like deposit with Homotrema sand. The Shell and Sand Sheet contains articulated Anomalocardia bivalves and moderate numbers of angular fragments (approximately 35%) that are likely from crab predation. Radiocarbon dates of articulated Anomalocardia specimens from the Shell and Sand Sheet range widely (approximately 4000 years), with shell condition (pristine to variably preserved) showing no correlation with age. The articulated condition of the bivalves with the wide-ranging dates suggests erosion and winnowing of the underlying Shelly Mud but minimal transport of the bivalves. The Shell and Sand Sheet has taphonomic characteristics indicative of a widespread tsunami overwash (sheet-like extent and articulated specimens) but lacks allochthonous reef-flat shells. Reef-flat shell material may not have penetrated the pond, as a tsunami would have to cross the reef-flat and overtop high dunes (2.2 m) hindering transport of larger shell material but allowing the Homotrema sand to penetrate. Processes including hurricane overwash, pond wave action, or tidal channel opening and closure are not favoured interpretations as they would not produce extensive sheet-like deposits. Taphonomic analysis is hampered by the limited (400–500 years BP) depositional history from Anegada’s ponds and the lack of comparative data from other Caribbean locations.


Mollusk taphonomy Event stratigraphy Hurricane Tsunami Caribbean 



The government of the British Virgin Islands provided access to Anegada’s salt ponds, use of airphotos, and guidance from its specialists in disaster management, surveying, and natural science. Among them, we especially thank Cynthia Rolli, Rondell Smith, Shannon Gore, and Dylan Penn. Lianna Jarecki shared her comprehensive knowledge of Anegada’s salt ponds, and Alejandra Rodriguez assisted with field work. Brian Atwater provided comments on early drafts of the manuscript. The work was supported in part by the Nuclear Regulatory Commission under its project N6480, a tsunami-hazard assessment for the eastern United States and NSERC Discovery grant to ER.


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Copyright information

© Springer Science+Business Media B.V. 2011

Authors and Affiliations

  • Eduard G. Reinhardt
    • 1
  • Jessica Pilarczyk
    • 1
  • Alyson Brown
    • 1
  1. 1.School of Geography and Earth SciencesMcMaster UniversityHamiltonCanada

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